Humans have used a variety of preserving techniques throughout history to keep food from spoiling. The advent of refrigeration has only been a relatively recent capability for us, in the grand scheme of things. For centuries we’ve had to rely on techniques like smoking, salting and sugar curing to preserve foods for later use. 

 Salt, sugar and smoke are commonly used as preservation methods. For example, corned beef uses large chunks of rock salt often referred to as ‘corns’ to preserve the meat. We are all familiar with modern jams and jellies, however these were originally developed as a way to preserve fruits from high harvest yields when refrigeration and modern, chemical-based preservatives were not available.

 The fundamental purpose of curing foods using preservation agents such as sugar is to inhibit the development of harmful food-borne pathogens like Salmonella or Clostridium botulinum and delay the spoilage of foods.

 How does sugar help preserve foods?

When sugar is added to fresh foods, like fruits and vegetables, it creates an osmotic effect. This means sugar absorbs water in the food resulting in the reduction of water activity (aw). Bacteria need water to grow and multiply, so lowering the water activity in a food product means there is less free water molecules for the bacteria. It creates an environment that limits microbial survival and growth.

In some foods, sugar facilitates the production of other substances that act as preservatives, like alcohol and acids. For example sugar is converted by fermentative yeasts to ethanol in wine, beer and other fermented drinks, or converted to organic acids like lactic acid in fermented foods such as sauerkraut, kimchi, pickles, sourdough bread, yogurts, miso and tempeh. In these cases, the alcohol or acid produced are both preservatives themselves.

Another example of using sugar as a preservative is the practice of ‘sugaring’. This involves desiccating food via dehydration and then packing it into a jar with crystalline sugar (table sugar) or a high density sugar liquid like honey or molasses. This helps to preserve fruits and vegetables by creating a low water activity environment that is hostile to microbial life.  

Can sugar alternatives be used as a preservative?

Sugar alternatives like sodium saccharin, aspartame and sucralose can pose a difficult challenge to food producers. These sugar alternatives change the overall chemical makeup of the food product which can have implications on shelf life, mouth feel and taste. These products often have to rely on other techniques, such as hot filling or acidity, or additives for preservation.

For more info, see Functions of Sugars In Food and Drinks

References

• Goldfein KR and Slavin JL. (2015). Why sugar is added to foods: food science 101. Comprehensive Reviews in Food Science and Food Safety, 14: 644 – 656.
• Smith AD and Stratton JE. (2007). Food Preservation, safety and shelf life extension. Institute of Agriculture and Natural Resources. University of Nebraska-Lincoln.